The mutation does not appear to be common — it was found in 2.4 percent of families with a history of breast cancer. But importantly, the mutation was not found in anyone without breast cancer in the study.

Because the study was conducted in Finland, future studies will need to investigatehow common the mutation is in other countries, said study researcher Roger Greenberg, an associate professor of cancer biology at the University of Pennsylvania School of Medicine.

In the future, women with a family history of breast cancer might be tested for the Abraxas mutation, Greenbergsaid.

Greenberg and colleagues found the Abraxas mutation in three of 125 breast cancer patients from families with a history of the condition. This gene had been suspected to play a role in breast cancer risk because it interacts with BRCA1.

When the researchers looked at an additional 991 breast cancer patients, they found the Abraxas mutation in one woman, who also turned out to have breast cancer in her family. None of the 868 healthy patients in the study had the Abraxas mutation.

The mutated Abraxas gene prevents cells from fixing damaged DNA, increasing the risk that a cell will become cancerous. The gene may increase the risk of other cancers as well. Indeed, one patient in the study was diagnosed with both breast andendometrial cancer, and some patients with the Abraxas mutation had family members with lung cancer, lip cancer and lymphoma.

More research is needed to know exactly how much of an increase in breast cancer risk the Abraxas mutation brings. But Greenberg noted women in the study with this mutation were diagnosed around the same age as those with BRCA1 and BRCA2 mutations — in their mid-40s.

Women with a mutation in BRCA1 or BRCA2 are about five times more likely to develop breast cancer in their lifetimes compared with women who do not have this mutation, according to the National Cancer Institute.

"Identifying more of these mutations will make it easier for patients to know their risk of developing breast cancer," said Dr. Kristin Byrne, chief of breast imaging at Lenox Hill Hospital in New York City, who was not involved in the study. Such genetic information may even help doctors better diagnose breast cancer. Most patients with the Abraxas mutation in the study had a type of breast cancer called lobular carcinoma, which is harder to detect on a mammogram. Knowing that a patient has this mutation might mean doctors use additional screening methods, such as MRI, Byrne said.

The study is published today (Feb. 22) in the journal Science Translational Medicine.

Pass it on:Some cases of hereditary breast cancer may be caused, in part, by mutations in a gene called Abraxas.